Recent investigations suggest that putative pain modulatory neurons (ON and OFF cells) in the rostroventral medulla receive cardiopulmonary input and may regulate arterial blood pressure as well as nociception. The overall objective of the present proposal, therefore, is to perform electrophysiological studies that quantitatively characterize the role of ON and OFF cells in the regulation of spinal nociception and arterial blood pressure. This will be accomplished by determining the degree of convergence of cardiopulmonary and somatic input to these neurons and by relating changes in neural activity to changes in arterial blood pressure and nociception. Somatic stimuli will include innocuous touch, noxious pinch, and noxious radiant heat. Cardiopulmonary stimuli will include electrical stimulation of cervical vagal afferents, pharmacological activation of vagal afferents, intravenous phenylephrine-induced increases in arterial blood pressure, and intravenous nitroprusside-induced decreases in arterial blood pressure. Tests of cardiopulmonary stimuli will be performed on both intact rats and rats with cardiopulmonary deafferentation. The specific aims of this proposal are to (1) quantitatively characterize the influence of either vagal or high pressure baroreceptor afferents on ON and OFF cells in the control of arterial blood pressure and the modulation of the nociceptive tail flick reflex, (2) quantitatively determine the contribution of the locus coeruleus/subcoeruleus and rostroventrolateral medulla to vagally- mediated changes in ON and OFF cells in spinopetal control of nociception, arterial blood pressure regulation, and visceral-visceral and visceral-somatic convergence.